Molecular sieves are a commercially important class of crystalline materials. They have distinct crystal structures with ordered pore structures which are demonstrated by distinct X-ray diffraction patterns. The crystal structure defines cavities and pores which are characteristic of the different species. Molecular sieves such as zeolites have been used extensively to catalyze a number of chemical reactions in refinery and petrochemical reactions, and catalysis, adsorption, separation, and chromatography.
One known molecular sieve for which a structure has been established is the material designated as RTH, which is a molecular sieve characterized by a two-dimensional pore system of intersecting 8-membered ring (8-MR) channels, leading to larger cages. Due to its unique structure, RTH framework type zeolites are of significant interest as catalysts for methanol-to-olefins (MTO) conversion and NOx reduction. Examples of RTH framework type materials include RUB-13 and SSZ-50.
S. Vortmann et al. (Micropor. Mesopor. Mater. 1995, 4, 111-121) disclose borosilicate zeolite RUB-13 and its synthesis using 1,2,2,6,6-pentamethylpiperidine and ethylenediamine as structure directing agents. Borosilicate zeolites, however, are not sufficiently catalytically active to be practicable for processes such as MTO conversion and NOx reduction.
U.S. Pat. No. 6,605,267 discloses aluminosilicate zeolite SSZ-50 and its synthesis using an N-ethyl-N-methyl-5,7,7-trimethyl-2-azonium bicyclo[4.1.1]octane cation as a structure directing agent.
The commercial development of SSZ-50 has been hindered by the high cost of the structure directing agent required for its synthesis and hence there is significant interest in finding alternative, less expensive means for the synthesis of aluminosilicate RTH framework type zeolites.
It has now been found that aluminosilicate RTH framework type zeolites can be prepared using 2,6-dimethyl-1-aza-spiro[5.4]decane cations as a structure directing agent.